150 research outputs found
On the Mass and Inclination of the PSR J2019+2425 Binary System
We report on nine years of timing observations of PSR J2019+2425, a
millisecond pulsar in a wide 76.5 day orbit with a white dwarf. We measure a
significant change over time of the projected semi-major axis of the orbit,
x-dot/x=(1.3+-0.2)x10^-15 s^-1, where x=(a sin i)/c. We attribute this to the
proper motion of the binary. This constrains the inclination angle to i<72
degrees, with a median likelihood value of 63 degrees. A similar limit on
inclination angle arises from the lack of a detectable Shapiro delay signal.
These limits on inclination angle, combined with a model of the evolution of
the system, imply that the neutron star mass is at most 1.51 solar masses; the
median likelihood value is 1.33 solar masses. In addition to these timing
results, we present a polarization profile of this source. Fits of the linear
polarization position angle to the rotating vector model indicate the magnetic
axis is close to alignment with the rotation axis, alpha<30 degrees.Comment: Accepted by Ap
Probing the Masses of the PSR J0621+1002 Binary System Through Relativistic Apsidal Motion
Orbital, spin and astrometric parameters of the millisecond pulsar PSR
J0621+1002 have been determined through six years of timing observations at
three radio telescopes. The chief result is a measurement of the rate of
periastron advance, omega_dot = 0.0116 +/- 0.0008 deg/yr. Interpreted as a
general relativistic effect, this implies the sum of the pulsar mass, m_1, and
the companion mass, m_2, to be M = m_1 + m_2 = 2.81 +/- 0.30 msun. The
Keplerian parameters rule out certain combinations of m_1 and m_2, as does the
non-detection of Shapiro delay in the pulse arrival times. These constraints,
together with the assumption that the companion is a white dwarf, lead to the
68% confidence maximum likelihood values of m_1 = 1.70(+0.32 -0.29) msun and
m_2 =0.97(+0.27 - 0.15) msun and to the 95% confidence maximum likelihood
values of m_1 = 1.70(+0.59 -0.63) msun and m_2 = 0.97(+0.43 -0.24) msun. The
other major finding is that the pulsar experiences dramatic variability in its
dispersion measure (DM), with gradients as steep as 0.013 pc cm^{-3} / yr. A
structure function analysis of the DM variations uncovers spatial fluctuations
in the interstellar electron density that cannot be fit to a single power law,
unlike the Kolmogorov turbulent spectrum that has been seen in the direction of
other pulsars. Other results from the timing analysis include the first
measurements of the pulsar's proper motion, mu = 3.5 +/- 0.3 mas / yr, and of
its spin-down rate, dP/dt = 4.7 x 10^{-20}, which, when corrected for kinematic
biases and combined with the pulse period, P = 28.8 ms, gives a characteristic
age of 1.1 x 10^{10} yr and a surface magnetic field strength of 1.2 x 10^{9}
G.Comment: Accepted by ApJ, 10 pages, 5 figure
Twenty-One Millisecond Pulsars in Terzan 5 Using the Green Bank Telescope
We have discovered 21 millisecond pulsars (MSPs) in the globular cluster
Terzan 5 using the Green Bank Telescope, bringing the total of known MSPs in
Terzan 5 to 24. These discoveries confirm fundamental predictions of globular
cluster and binary system evolution. Thirteen of the new MSPs are in binaries,
of which two show eclipses and two have highly eccentric orbits. The
relativistic periastron advance for the two eccentric systems indicates that at
least one of these pulsars has a mass >1.68 Msun at 95% confidence. Such large
neutron star masses constrain the equation of state of matter at or beyond the
nuclear equilibrium density.Comment: 12 pages, 2 figures. Accepted by Science. Published electronically
via Science Express 13 Jan 200
Toward an Empirical Theory of Pulsar Emission XII: Exploring the Physical Conditions in Millisecond Pulsar Emission Regions
The five-component profile of the 2.7-ms pulsar J0337+1715 appears to exhibit
the best example to date of a core/double-cone emission-beam structure in a
millisecond pulsar (MSP). Moreover, three other MSPs, the Binary Pulsar
B1913+16, B1953+29 and J1022+1001, seem to exhibit core/single-cone profiles.
These configurations are remarkable and important because it has not been clear
whether MSPs and slow pulsars exhibit similar emission-beam configurations,
given that they have considerably smaller magnetospheric sizes and magnetic
field strengths. MSPs thus provide an extreme context for studying pulsar radio
emission. Particle currents along the magnetic polar flux tube connect
processes just above the polar cap through the radio-emission region to the
light-cylinder and the external environment. In slow pulsars radio-emission
heights are typically about 500 km around where the magnetic field is nearly
dipolar, and estimates of the physical conditions there point to radiation
below the plasma frequency and emission from charged solitons by the curvature
process. We are able to estimate emission heights for the four MSPs and carry
out a similar estimation of physical conditions in their much lower emission
regions. We find strong evidence that MSPs also radiate by curvature emission
from charged solitons.Comment: 14 pages, published in Ap
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